Technological Potential and Challenges to Low GHG Transportation

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Technological Potential and Challenges to Low GHG
Transportation
C. F. Edwards Dept. of Mechanical Engineering and
Global Climate and Energy Project Stanford
University IPIECA Transportation and Climate
Change Conference, October 13, 2004
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United States CO2 Emissions by Sector and Fuels
2000
Millions of metric tons per year carbon equivalent
700
43
Natural Gas
600
Petroleum
32
500
Coal
400
300
15
200
7
100
4
0
Residential
Commercial
Industrial
Transportation
Electric
Generation
Source U.S. EPA Inventory of Greenhouse Gas
Emissions, April 2002
3
13
32
12
27
49
56
Source OECD/IEA, Paris, World Energy Outlook
2002, Second Edition, November (2002)
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Brainstorming on Approaches

• No carbon in fuel
• hydrogen, other carrier?
• Less carbon in fuel
• natural gas, methanol, DME, other carrier?
• Use less fuel
• conservation, efficiency, mass transit
• Capture carbon from fuel
• separation, on-board storage, collection
  stations, transport, sequestration,
• Cycle fuel carbon through environment
• biofuels, solar methanol (Nate Lewis), gasoline
  with remediation elsewhere (Klaus Lackner),

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Efficiency

• Efficiency How well we use energy to accomplish
  a specified task. (Not the same as
  conservation.)
• Carrier efficiency measures how well the energy
  of a resource is converted to an energy carrier
  (i.e. a fuel)
• Conversion efficiency measures how well carrier
  energy is converted to entropy-free energy (work,
  KE, PE).
• Utilization efficiency measures how well
  entropy-free energy is applied to a specified
  task.
• Environmental efficiency measures the
  expenditure of entropy-free energy required to
  integrate the specified task into our environment
  in an acceptable way.

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Source M.L. Wald, Questions About a Hydrogen
Economy, Scientific American, May, 2004
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Conversion Efficiency of Engines
50
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Conversion Efficiency Current I.C. Engines
Heat Loss
CI
Stability, Emissions, Power

• Gasoline (SI)
• Homogeneous Charge
• Spark Ignition
• NO, HC, CO2
• Diesel (CI)
• Inhomogeneous Charge
• Compression Ignition
• NO, Soot, CO2

Knock
SI
(from Taylor, 1985)
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Propulsion Efficiency Aircraft
Source J.D. Mattingly, Elements of Gas Turbine
Propulsion, McGraw Hill (1996)
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Propulsion Efficiency Automobiles
0.1 0.2 0.3 0.4
0.5 0.6
0.7
PEM
CI
A well-to-tank efficiency of 62 for hydrogen,
85 for Diesel gives a well-to-wheel efficiency
of 36 for both CI and PEM at hp 90.
SI
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Environmental Efficiency

• 100 for hydrogen if carbon-free (I know of no
  source that is carbon-free today.)
• ltlt100 for IC engines with fossil fuels and for
  hydrogen with carbon release
• What can be done about the 1/3 of carbon
  emissions due to transportation if we do not
  pursue carbon-free hydrogen?

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What Limits I.C. Engine Efficiency?

• Not Carnot!
• Applies only to Heat Engines (not Reactive
  Engines)
• Limiting factor is the inability to destroy
  entropy

Energy
Entropy
Efficiency
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Reactive Engine Efficiency

• Reactive engines use chemical energy (not heat)
• Limiting factor is still the inability to destroy
  entropy

Energy
Entropy
Efficiency
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Ideal Process Paths
Adiabatic Reversible Compression
Adiabatic Reversible Expansion
Adiabatic Reaction
Isothermal Reaction
Isothermal Reaction w/Work
Adiabatic Reversible Reaction
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The Fuel Cell is a Reversible Combustion Engine

• Catalysts allows the half-cell reactions to occur
  reversibly
• Restraint is provided by controlling electron
  transfer
• The load must provide the restraint!

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Conversion Efficiency Potential
Stoichiometric Hydrogen/Air
CI
SI
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Concluding Remarks

• Conversion efficiency of transportation engines
  is poor in comparison to theoretical limits.
  Misconceptions about the true limits have led to
  stagnation of innovation. (Improvement by a
  factor of 2 is possible.)
• Propulsive efficiency of current vehicles is
  poor. Developments in hybrid technology are
  beginning to address this now. (Improvement by
  a factor of 2 is possible.)
• A significant component of propulsive efficiency
  is regeneration. Without this component, maximum
  propulsion efficiency is less than 50.
• Environmental Efficiency is the key to closing
  the loop in your thinking about energy
  technologies
• Not wells-tank-wheels
• But environment-wells-tank-wheels-environment

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Reversibility

• Reversibility requires that you act with
  restraint
• Restrained action is possible only with a
  suitable device

Compression/Expansion
Gas Mixing
Piston/Cylinder
Semipermeable Membrane
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Efficiency Limits Driving Cycles
FTP/Urban Dynamometer Driving Cycle

• Work is required to
• overcome drag
• accelerate
• Work is available from
• engine
• stored KE
• There is assumed to be no change in potential
  energy.

Distance 11.0 miles Time 1875 s Avg.
Speed 21.2 MPH
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Efficiency Limits Power Reqd
FTP/Urban Dynamometer Driving Cycle

• Consider a small family automobile
• 13 RLHP _at_ 55 MPH
• (10 RR _at_ 55 MPH)
• 2643 lb (1200 kg)
• Cycle Work
• Road-Load 3.1 MJ

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Efficiency Limits Power Reqd
FTP/Urban Dynamometer Driving Cycle

• Consider a small family automobile
• 13 RLHP _at_ 55 MPH
• (10 RR _at_ 55 MPH)
• 2643 lb (1200 kg)
• Cycle Work
• Road-Load 3.1 MJ
• Acceleration 3.7 MJ
• The work required to overcome drag must be
  supplied by the engine.
• The work required for accel. can be supplied by
  regeneration.

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Efficiency Limits Fuel Economy

• Recognizing that DHc DGc Exergy (work
  potential)
• Max fuel economy for FTP/UDDS
• Without regeneration 189 MPG
• With regeneration 416 MPG
• Max fuel economy for HWFET
• Without regeneration 171 MPG
• With regeneration 213 MPG
• Without regeneration, the highest propulsive
  efficiency possible for each cycle is
• FTP/UDDS 45.4
• HWFET 80.3